A dynamic-link library (DLL) is a module that contains functions and data that can be used by another module (application or DLL). It is Microsoft's implementation of the shared library concept in the Microsoft Windows and OS/2 operating systems.
A dynamic-link library (also written without the hyphen), or DLL, is Microsoft's implementation of the shared library concept in the Microsoft Windows and OS/2 operating systems. This type of library usually has the file extension DLL, OCX (for a library containing ActiveX controls), or DRV (for a legacy system driver). The file formats for DLLs are the same as for Windows EXE files — that is, Portable Executable (PE) for 32-bit and 64-bit Windows, and New Executable (NE) for 16-bit Windows. As with EXEs, DLLs can contain code, data, and resources, in any combination. In the broader sense of the term, any data file with the same file format can be called a resource DLL. Examples of such DLLs include icon libraries
A DLL is a library that contains code and data that can be used by more than one program at the same time. For example, in Windows operating systems, the Comdlg32 DLL performs common dialog box-related functions. Therefore each program can use the functionality that is contained in this DLL to implement an Open dialog box. This helps promote code reuse and efficient memory usage.
By using a DLL, a program can be modularized into separate components. For example, an accounting program may be sold by module. Each module can be loaded into the main program at run time if that module is installed. Because the modules are separate, the load time of the program is faster, and a module is only loaded when its functionality is requested.
